Ultra high frequency tuning unit



Dec. 31, 1946. J. K. JOHNSON ULTRA-HIGH-FREQUENCY TUNING UNIT Filed Oct. 3, 1942 FIG.4

-w w ae ar UIIIIIII 5 G 00 Rotation ofMember l3 F G 5 cuavo A 2 W F INVENTOR JOHN KELLY JOHNSON BY W f ATT RNEY Patented Dec. 31, 1946 ULTRA HIGHFREQUENCY TUNING UNIT John Kelly Johnson, Deer-field, Ill., assignor, by mesne assignments, to Haz'eltine Research, Inc., Chicago, 111., a corporation of Illinois Application October 3, 19 12, Serial No. 460,645

6 Claims. 1

The present invention relates to ultra-highfrequency tuning, units for wave-signal apparatus and, particularly, to suchunitsofthe type wherein tuning over a relatively wide frequency band is effected primarily by variation of inductance of a resonant-tuned circuit..

Inductively-tuned resonant circuits have an average value of resonant impedance higher than that which can be obtained by a condenser-tuned circuit tunable over the same frequency band. Whereas condenser-tuned circuits have minimum impedance at the low-frequency end of a tuning band and high impedance at the highfrequency end, the inductively-tuned circuit conversely has minimum impedance at the high-frequency end and maximum impedance at the lowfrequency end of the band- This characteristic of inductively-tuned circuits has particular importance, for example, in ultra-high-frequency oscillators where, the low impedance of a condenser-tuned circuit frequently causes the oscillator to cease to function near the low-frequency end of its operatingef'requency band. The minimum impedance of an inductively-tuned circuit, on the other hand, is relatively high so that the operation of the oscillator is generally dependable over its entire frequency range.

Ultra-high-frequency tuning. unit of the inductive tuning type generally are of quite low ohmic resistance to enable them to have a desirable high ratio of inductive reactance to resistance. They consequently involve the use ofelectri'cal conductors of relatively large cross section. The length of the conductor is generally only a matter of inches since it must havean inductance of the order of a few microhenries. It. is generally'quite desirable that such tuning. units do not involve the use of either-flexibl pigtails or sliding contacts- The prior art low-frequency arrangements forv effecting inductive-tuning without sliding contacts or flexible pigtails involve inductors of relativelylarge-inductance, few types of which are well adapted forultra-high-frequency inductive tuning. One such prior art arrangement isthe powdered iron-core type of inductor. The. latter, when used at ultrahigh-frequencies, presents difficulty in obtaining a sufliciently high ratio of inductive reactance to resistance (high Q), cannot generally be built witha. desirable de- P greeofruggedness of construction,. and requires afairly massive core.

It is an objectof thepresent invention, therefore, to provide. a new and improved ultra-highfrequency tuning unit. which avoidsone or more of the disadvantages and limitations of the prior art arrangements of this type.

It is a further object of the invention to provide a new and improved ultra-high-frequency tuning unit having a light weight, ruggedness and rigidity, and one readily adapted to be manufactured within close tolerances in large quantities at low cost.

It is an additional object of the invention to provide an ultra-high-frequency' tuning unit for inductive tuning and adapted to have a high ratio of inductive reactance to resistance, that is, a high Q, and one possessing electrical symmetry and balance.

It is a further object of the invention to provide an ultra-high-frequency tuning unit in which its point of mechanical support provides a convenient point at which to establish a radio-frequency neutral point while preserving mechanical symmetry and electrical balance relative thereto.

In accordance with the invention, an ultrahigh-frequency tuning unit comprises a singleturn loop member of conductive material having a predetermined cross-sectional circumference, the loop member having at least two spaced terminal points thereon. The tuning unit includes a rotatable member comprising a ring of conductive material having a cross-sectional circumference at least as large as that of the loop member, and means for supporting. the rotatable member within the stationary member for rotation about a diameter thereof symmetrical with respect to the terminal points comprising a shaft journalled in the stationary member in electrical contact therewith and mechanically and electrically connected to' the rotatable member. The average minimum spacing of the rotatable member fromthe stationary member is appreciably less than the aforementioned circumference. The stationary member is thereby adapted to be elec-- trically connected to ground in the vicinit of the shaft to provide a tuning unit electrically balanced to ground and the rotatable member, upon rotation, is effective substantially to vary the inductanceof the stationary'member while maintaining the electrical balanceto ground;

For a better understanding of the present in-- vention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, Fig. 1- illustrates an ultra-high-frequency tuning unit embodying the present invention; Fig. 2- is anexploded view showing the assembly of the tuning-unit rotor member and shaft; Fig. 2A is a cross-sectional view taken along the line B-B of Fig. 2; Fig. 3 is a top view, partly in cross section, of the tuning unit of Fig. 1; Fig. 4 is a circuit diagram of an ultra-high-frequency oscillator which utilizes the tuning unit of the present invention; while Fig.6 isa graph representing the manner in which the operating frequency of the Fig. 4 oscillator varies with rotation of the tuning-unit rotatable member.

Referring now more particularly to Fig. 1 of the drawing, there is illustrated an ultra-highfrequency tuning unit embodying the present in- Vention in a preferred form. The tuning unit comprises a stationary single-turn loop member If! comprising a ring of conductive material having a substantially circular cross section of relatively large area and of predetermined crosssectional circumference. There is secured to the member I!) stiffening side flanges II, II, useful primarily to give added rigidity to member I0, and a base member l2 for securing the tuning unit to a suitable support. The stationary member III, the flanges II, II and the base member I2 are preferably formed of aluminum by die casting. This material has the advantages that it provides a tuning unit of very light weight, is adapted to be easily die cast, and has high electrical conductivity, thus enabling the attainment of a high ratio of inductive reactance to resistance, or high Q, for the tuning unit. Die casting is desirable from the standpoint that tuning units embodying the invention may be manufactured within close tolerances in large quantities at low cost.

The diameter of the loop'member I9 is, of course, governed by the desired operating, frequency range considered in connection with the total capacitance of the circuit which will be connected across the open ends of the member ID. The factors affecting choice of a suitable diameter are well understood and such diameter may readily be determined by one skilled in the art.

The large cross section of the conductive material of the loop member Ill aids in attaining a high ratio of inductive reactance to resistance, and thus a high Q, for the tuning unit. Variations of crosssection have only a second-order effect on the inductance of the member It. In the ultra-high-frequency range for which the tuning unit of the present invention is particularly suited, for example tuning ranges of. the

order'of and above 100 megacycles, the highfrequency current penetrates the loop member ID to only -a very small depth. For thisreason, the member I may be constructed of hollow tubing, if desired, without materially impairing the Q-of the tuning unit. This in general, however, willincrease the cost of the unit since die casting cannotbe used'with this construction. It has been found that the Q of the tuning unit is slightly improved by omission of the stiffening flanges I I, I I and this may be done in a particular application where the loop member II] has sumcient rigidity without the use of the flanges.

The tuning unit also includes a member I3 comprising a ring of conductive material preferably having a substantially circular cross section of relatively large cross-sectional area equal at least to that of the stator member III. A largecrosssectional area of the material of the rotatable member I3 aids in attaining a high ratio of in-' 4 ductlve reactance to resistance for the tuning unit.

The tuning unit also includes means for supporting the members I0 and I3 for relative move ment to vary the spacing therebetween. In the particular construction shown, the member I3 is supported within the stationary member In for rotation about a diameter thereof. This means comprises a web l4, integrally formed with the rotatable member I3, and a shaft I5 journalled in an aperture l6 provided in the stationary member Ill and base member I2. The shaft I5 is in electrical contact with the stationary member l0 and is mechanically and electrically connected to the rotatable member I3 by rivets I1, I! which secure the shaft I5 to the web I4. The web I4 and ring 13 are preferably formed as an integral member of aluminum by die casting.

The preferred manner of assembling the shaft l5 and rotatable member I3 is best shown by the exploded views of Figs. 2 and 2A, of which Fig. 2A is a cross-sectional view taken along the line BB of Fig. 2. The shaft I5 is provided with a slotted end E8 to receive the web It of the rotatable member and is inserted through a collar I9 integrally formed with the rotatable member l3. Suitably spaced holes 20 are provided in the shaft I5 and web I4 to receive the rivets I1, I? which secure the shaft and rotatable member in assembled relation. It will be understood, of course, that the assembly of the shaft IS with the rotatable member I3. is performed while the rotatable member I3 is positioned within the stationary member I0.

The rotatable member I3 is adapted upon rotation to vary the inductance of the stationary member ID. In order that an appreciable variation of the inductance of the stationary member IE may be effected within the range of rotation of the rotatable member IS, the average minimum spacing of the rotatable member is from the stationary member l0 should be appreciably less than the cross-sectional circumference of the material of the stationary member I ii and preferably is less than one-third of suchcircumference. As previously stated, the highefrequency' current penetrates the loop member Iii only to a very small depth and hence flows almost entirely on its surface. For this reason, the circumference of the material of member If! is an important factor in regard to the minimumaverage spacing of members Iii and I3 and this is true whether the member Ill be formed of awide and relatively thin strip-like material or of a material having a circular cross section, as shown. Specifically, if the conductive material of the stationary member III has a thickness of predetermined value in the plane of the member H], or is of circular cross section with a predetermined cross-sectional diameter, the minimum spacing of the rotatable member I3 from the stationary member lfl should be not appreciably greater than the predetermined value of thickness or cross-sectional diameter. In general, the closer the minimum spacing of the rotatable member l3 from the stationary member I I], the greater will be the variation of inductance of the stationary member ID within the range of rotation of the rotatable member l3.

While the shaft I5 need not be J'ournalled in the stationary member I0 at a point diametrically opposite the gap between the ends of the latter, thisconstruction is desirable from the standpoint that the rotatablev member I3 is supported symmetrically about a diameter of the stationary member I i! and rotatesabout such diameter, thus providing a tuning unit which is mechanically and electricall balanced. Consequently, the tuning unit is electrically balanced to ground when a ground connection is made thereto through the supporting member l2, as by mechanically and electrically connecting the member l2 to a grounded metal panel of an ultra-high-frequency apparatus.

The ends of the stationary tuning member in are, in most applications, coupled through small condensers to one or more electrodes of a vacuum device included in an ultra-high-frequency apparatus. The tuning unit of the present invenvtion has the advantage that these coupling condensers may easily and readily be constructed on the end portions of the stationary member ID. This construction is highly desirable from the standpoint that it provides a minimum of stray circuit inductance, the latter being quite troublesome and very undesirable at ultra-high-frequencies. This construction is best shown in Fig. 3, which is a top view, partly in cross section, of the tuning unit shown in Fig. 1. Each such coupling condenser comprises an end portion of the flange II as a plate thereof, a second condenser plate 2|. conveniently formed of thin-tinned copper having a connecting lug 22 formed as an integral part thereof, and a suitable sheet of dielectric 9, which may be a sheet of mica, for separating the condenser plate 2| from the end portion of the flange I I. The coupling condenser is maintained in assembled relation by machine screws 23 which are threaded into the flange H and are electrically insulated by insulating bushings 24 from the condenser plate 2|. In the event that the stiffening flanges H are omitted from the tuning unit, as may be desirable in certain applications as hereinbefore suggested, the coupling condenser is formed directly upon an end portion of the stationary member Ill. In this case, the condenser plate 2| preferably is formed to have a contour corresponding to that end portion of the stationary member ID over which the condenser plate 2| is secured. A coupling condenser of increased capacity may be had by adding additional dielectric sheets and condenser plates, as desired.

Fig. 4 represents a circuit diagram of an ultrahigh-frequency oscillator and illustrates one application of the tuning unit of the present invention. The inductor ||'||3 of this arrangement schematically represents the stationary member Ill of the tuning unit, the inductance of which is variable, as indicated by the arrow, by virtue of the effect of the rotatable member l3 on the stationary member In. The inductor |0-|3 is grounded at its center point, as by grounding the supporting member l2 of the tuning unit, and is tunable to a desired operating-frequency band by a fixed condenser 25 shown in broken lines for the reason that it may be comprised in whole or in part of the inherent structure and circuit capacitance existing between the end terminals of the stationary loop member Ill. The oscillator includes a vacuum tube 26 having its anode coupled through one of the coupling condensers ||2| to one end of the inductor ||l| 3 and having a control electrode coupled through a second coupling condenser ||-2| to the other terminal 0f the inductor Ill-l3. It will be understood that the coupling condensers ||-2| are constructed on individual end portions of the stationary loop member |0 of the tuning unit as previously described. The anode of the vacuum tube 26 is energized through a suitable radio-frequency choke 21 from a source of energizing potential, indicated as. +3, and the control electrode of the vacuum tube is connected to ground through a suitable radio-frequency choke 28 and a grid-leak resistor 29. The cathode of the vacuum tube is connected to ground through a radiofrequency choke 30 and the heater of the tube is energized through the choke 30 and a radio-frequency choke 3| from a suitable source of energizing potential indicated as +A. A condenser 32 is connected between the anode and cathode of tube 26 and a condenser 33 between the control electrode and cathode thereof, the condensers 32 and 33 being shown in broken lines for the reason that they may be comprised in whole or in part of the inherent interelectrode capacitances existing between the anode, cathode, and control electrode of this tube.

Considering now the operation, of the Fig. 4 oscillator arrangement, oscillatory voltages developed across the resonant circuit Ill-l3 and 25 produce corresponding potentials across the condensers 32 and 33 which are coupled in series across the resonant circuit, The voltage developed across the condenser 33 and applied to the s, control electrode and cathode of tube 26 is effectively a voltage fed back to the control electrode from the output circuit of this tube and has such phase respect to the voltage developed in the latter circuit that it is efiective to produce sustained oscillations in the resonant circuit ||l-|3 .25. A certain portion of the voltage developed in the output circuit of tube 26 may also be fed back through the inductor |B|3 to the control electrode of tube 26, thus being also effective to produce sustained oscillations in the resonant circuit, but it is believed that the major portion of the feed-back voltage is that across the condenser 33. It will be understood that the frequency of oscillation of the resonant circuit Ill-l 3 and is determined by suitable adjustment of the rotatable member 3 with respect to the loop member it to provide the desired value of inductanee for operation at the desired operating frequency.

. mal to that of the stationary member It. It will be apparent from this graph that the resonant frequency of the tuning unit varies approximately linearly with angular variations of its rotatable member l3 over a considerable range of variation of the latter.

A illustrative of a specific embodiment of the invention, the following parameters are given for an embodiment of the invention of the type shown in Fig- 12 Stationary member ii, of die-cast aluminum:

Diameter of circular cross section inches Spacing of nds of member |il do- External d i a m e t e r of member in inches 2% Rotatable member I3, of die-cast aluminum:

Diameter of circular cross section inches External diameter -do 1% .ing a simple ring of conductive material.

cillator megacycles Approximately 150-200 While the movable member l3 of the tuning unit of the present invention is shown as rotatable about a diameter of the stationary member 10, it will be evident that the member l3 need not be rotatable but may, if desired, be moved axially with respect to the member l0. In fact, the member l3 may b the stationary member and the member It the movable member, the latter then having either rotatable or axial movement relative to member i3. Further, the members 10 and i3 may be interchanged without departing from the invention, the inner member then becoming the open-circuited single-turn loop and the outer member the closed-circuit member which varies the inductance of the inner loop member upon relative movement of the members. Additional 1y, while the members 10 and I3 are shown as ring-shaped members, it will be apparent that these members may have other configurations, for example elliptical or square or may even have configurations different from each; other, although in general the greatest variation of inductance of the loop member is eifected when the two members have the same configuration.

Moreover, while the single-turn loop member Iii is shown as bein of the open-circuited type, it will be understood that it may also, like the member i3, be of the closed-circuit type compris- In this event, the tuning unit of the invention is suitable for operation at much higher frequencies where waves of current or voltage are produced around the periphery of the loopmember ID, the

loop member being coupled to associated apparatus in any suitable well-known manner.

From the above description of the invention, it will be apparent that a tuning unit embodying the invention has the advantages of very light weight, great ruggedness and rigidity, and is one readily adapted to be manufactured within close tolerances in large quantities at low cost. The tuning ,unit of the invention also has the advantags that it is adapted to have a high ratio of inductive reactance to resistance, or high Q, and possesses electrical and mechanical symmetry and balance. A radio-frequency ground connection is readily made to the unit while preserving mechanical symmetry and electrical balance to ground. The tuning unit of the invention has the additional advantages that a wide variation of inductance of the unit may be effected in continuous manner between minimum and maximum values and without the need of any sliding contacts or flexible pigtails.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein-without departing from the Gil invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and'scope of the invention.

What is claimed is:

1. An ultra-high-frequency tuning unit comprising, a stationary single-turn loop member including a ring of conductive material having a substantially circular cross section of predetermined radial diameter, said loop member having at least two spaced terminal points thereon, a rotatable member comprising a ring of conductive material having a substantially circular cross section at least substantially as large as that of said loop member, and means for supporting said rotatable member within said stationary member for rotation about a diameter thereof symmetrical with respect to said terminal points including a shaft journalled in said stationary member in electrical contact therewith and mechanically and electrically connected to said rotatable member, the average minimum spacing of said rotatable member from said stationary member being not greater than one-half said radial diameter, whereby said stationary member is adapted to be electrically connected to ground in the vicinity of said shaft to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member while maintaining said electrical balance to ground.

2. An ultra-high-frequency tuning unit comprising, a stationary single-turn loop member including a ring of conductive material having a thickness of predetermined value in the plane of said member and a predetermined cross-sectional circumference, said loop member having at least two spaced terminal points thereon, a rotatable member including a ring of conductive material having a cross-sectional circumference at least as large as that of said loop member, and means for supporting said rotatable member within said stationary member for rotation about a diameter thereof symmetrical with respect to said terminal points including a shaft journalled in said stationary member in electrical contact therewith and mechanically and electrically connected to said rotatable member, the average minimum spacing of said rotatable member from said stationary member being not greater than one-half said predetermined value of thickness, whereby said stationary memher is adapted to be electrically connected to ground in the vicinity of said shaft to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member while maintaining said electrical balance to ground.

3. An ultra-high-frequency tuning unit comprising, a stationary single-turn loop member including a ring of conductive materialhaving a circular cross section of predetermined diameter, said loop member having at least two terminal points thereon, a rotatable member including a ring of conductive .material having a circular cross section of diameter not substantially less than said predetermined diameter, and means for supporting said rotatable member within said stationary member for rotation about a diameter thereof symmetrical with respect to said terminal points including a shaft journalled in said stationary member in electrical contact therewith and mechanically and electrically connected to said rotatablemember, the average minimum spacing of said rotatable member from said stationary member being appreciably less than onehalf said predetermined diameter, whereby said stationary member is adapted to be electrically connected to ground in the vicinity of said shaft to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member while maintaining said electrical balance to ground.

4. An ultra-high-frequency tuning unit comprising, a stationary single-turn loop member ineluding a ring of conductive material having a predetermined cross-sectional circumference, said loop member having at least two spaced terminal points thereon, a rotatable member including a ring of conductive material having a cross-sectional circumference at least as large as that of said loop member, and means for so mechanically supporting said members that said loop member is effectively electrically symmetrical with respect to said terminal points and said rotatable member rotates about a diameter of said loop member to vary the spacing therebetween while maintaining said electrical symmetry, said supporting means including a shaft journalled in said stationary member in electrical contact therewith at a point equidistant from said terminal points and mechanically and electrically connected to said rotatable member, the average minimum spacing of said rotatable member from said stationary member being appreciably less than said circumference, whereby said stationary member is adapted to be electrically connected to ground in the vicinity of said shaft to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member while maintaining said electrical balance to ground.

5. An ultra-high-frequency tuning unit comprising, an open-circuit single-turn loop member including a ring of conductive material having a predetermined cross-sectional circumference, the end terminal portions of said loop member being relatively closely spaced, a pair of coupling condensers each including an individual one of said end portions as a plate thereof, a rotatable member including a ring of conductive material having a cross-sectional circumference at least as large as that of said loop member, and means for supporting said rotatable member within said stationary member for rotation about a diameter thereof symmetrical with respect to said end portions including a shaft journalled in said stationary member in electrical contact therewith and mechanically and electrically connected to said rotatable member, the average minimum spacing of said rotatable member from said stationary member being appreciably less than said circumference, whereby said stationary member is adapted to be electrically connected to ground in the vicinity of said shaft and is adapted to be coupled by said coupling condensers to a wave signal-translating circuitelectrically balanced to ground to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member While maintaining said electrical balance to ground.

6. An ultra-high-frequency tuning unit comprising, a stationary single-turn loop member comprising a ring of conductive material having a predetermined cross-sectional circumference, said loop member having at least two spaced terminal points thereon, a rotatable member comprising a ring of conductive material having a cross-sectional circumference at least as large as that of said loop member, and means for support ing said rotatable member within said stationary member for rotation about a diameter thereof symmetrical with respect to said terminal points comprising a shaft journalled in said stationary member in electrical contact therewith and mechanically and electrically connected to said rotatable member, the average minimum spacing of said rotatable member from said stationary member being appreciably less than said circumference, whereby said stationary member is adapted to be electrically connected to ground in the vicinity of said shaft to provide a tuning unit electrically balanced to ground and said rotatable member, upon rotation, is effective substantially to vary the inductance of said stationary member while maintaining said electrical balance to ground.

JOHN KELLY JOHNSON. 

